The invention relates to a diagnostic system for a valve and, more particularly, to a closing valve or a control valve, which can be actuated by a drive and installed in a pipeline, and to a diagnostic method, which can be executed with the diagnostic system.
In many areas of process engineering and power engineering, the trouble-free operation of a plant depends on the flawless functioning of the control, check, closing and regulating valves used. To avoid costly irregular operational interruptions, any valve damage should, where possible, be detected early, i.e., before a valve failure can cause the plant to be shut down. Defective valve seats cause, for example, leakage flows or leaks, which emit broadband noise. Recording and evaluating the sound emission of a valve can thus be used for early detection of valve damage. Since valve damage can lead to errors and expensive follow-up costs, a diagnosis, possibly with automatic detection and programmable evaluation of the errors, is of great benefit. Statistical evaluations of the diagnostic data can be used to optimize maintenance processes to ensure a timely replacement of a faulty valve and to qualitatively evaluate and classify valve manufacturers or to evaluate the suitability of specific valves for different process types.
DE 199 24 377 A1 discloses a diagnostic system for a valve that can be actuated by a position regulator through a drive. This diagnostic system has a facility for detecting, storing and evaluating solid-borne sound spectra measured at the valve. To enable a particularly reliable valve diagnosis, a solid-borne sound spectrum detected with a slightly open intact valve can be stored in the detection, storage and evaluation facility. For diagnosis purposes, a solid-borne sound spectrum detected with the valve closed is compared with the stored spectrum, and the similarity is used as a criterion for the lack of leak tightness of the valve.
DE 199 47 129 A1 discloses a further diagnostic system for a valve. The possibilities cited for attaching a sensor for solid-borne sound are the outer wall of the valve housing, the yoke between the valve housing and drive, the connecting flange between the yoke and housing, the flanges between the housing and pipeline and the valve stems. A measurement signal, supplied by the sound sensor, is fed to an evaluation facility, which is located in the housing of the valve position regulator or can be disposed separately from the housing of the valve position regulator. One problem here is that the sound sensor supplies a measurement signal with a relatively low sound level, which can only be transmitted without interference to the evaluation facility with a certain outlay.
Alternatively, it is possible to dispose the sensor in or on the housing of the evaluation facility, which is then connected to the valve in a sound-conducting manner. This has the advantage that the short distance between the evaluation facility and the sensor means that relatively short connecting lines are required. An exemplary electrical measurement signal is therefore subject to only minor attenuation on the transmission path and can be protected against the coupling in of interference without major outlay because of the small spatial dimensions. The diagnostic system can also be fitted particularly easily on a valve, because there is no need to lay cables outside the housing of the evaluation facility or to separately fit the sensor for solid-borne sound to the valve. Ultrasound emissions, which occur predominantly in the region of the closing body, are coupled into the sound sensor as sound signals by the valve housing, a flange generally disposed between the valve housing and a yoke, and by the yoke itself, where the sound sensor is generally located in or on the housing of the evaluation facility, which is generally screwed onto the yoke. The measurement signal therefore reaches the housing of the evaluation facility in acoustic form rather than electrical form, with acoustic/electrical signal conversion being performed with the solid-borne sound sensor in the housing.
The known diagnostic systems share a common feature in that the diagnosis can only be made based on a relatively complex analysis of the recorded solid-borne sound signal and that they can only be used to determine the presence of a leak. The known diagnostic systems do not, however, allow a quantitative analysis of the leak.